1. Field of the Invention
The present invention relates to a plate straightening machine for straightening plates, such as thin and thick plates, with rolls.
2. Description of the Related Art
Straightening machines have a stand into which a group of upper work rolls and a group of lower work rolls are built. The upper and lower work rolls are appropriate combinations of various rolls, such as small, intermediate and large work rolls, including back-up rolls. The upper and lower rolls straighten bends in strips.
Because the lower rolls of such a straightening machine are moved up and down by a pressure device, they can be easily replaced with new rolls. However, because the upper rolls are fixed, it is difficult to replace and maintain them. In order to easily replace and maintain the upper rolls, an upper frame over which the upper rolls are installed is rotated upwardly through 180.degree. in a path in which strips are fed (in a path direction) from an operating position, at which the upper rolls face downward, to a non-operating position, at which the upper rolls face upward.
To replace the upper rolls, the upper rolls in the non-operating position are removed and are carried by a crane to a spot where they are replaced with new rolls. The new rolls are carried by the crane onto the upper frame and are then mounted thereon.
However, such a replacing method is troublesome and time-consuming. Since replacement of the upper rolls are carried out above a strip, dust on the upper frame and other components fall onto the strip, thus staining it. In addition, it is dangerous to replace upper rolls because they are carried by a crane.
There is a type of straightening machine in which the replacement of upper rolls is carried out quickly in the following way. The upper rolls are installed on a common mounting plate which is replaced with a new mounting plate. This replacing method, however, has the same problems, for the same reason, as the previous method, e.g., it is troublesome and time-consuming, and a strip may be stained. This method is also dangerous because mounting plates are carried by a crane.